Solutions Question 376

Question: 0.5 m solution of a complex of iron and cyanide ions has the depression of f.pt. to be 3.72 K ( $ K_{f} $ For water $ =1.86Kmola{l^{-1}} $ ). The formula of the complex is:

Options:

A) $ K_4[Fe{{(CN)}_6}] $

B) $ K_2[Fe{{(CN)}_4}] $

C) $ K_3[Fe{{(CN)}_6}] $

D) $ Fe{{( CN )}_4} $

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Answer:

Correct Answer: C

Solution:

$ \Delta T_{f}(normal)=K_{f}m=1.86\times 0.5=0.93{}^\circ $ Assuming 100% ionization, i = n = No. of ions per molecule $ =\frac{Observed,\Delta T_{f}}{Normal,\Delta T_{f}}=\frac{3.72}{0.93}=4 $

$ K_3[Fe{{(CN)}_6}]\xrightarrow{{}}3{K^{+}}+{{[Fe{{(CN)}_6}]}^{3-}} $ No. of ions = 4



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